Severe acute respiratory syndrome (SARS) is a lower respiratory disease with approximately 10% mortality that emerged in the Guandong province of China in 2002. The disease is caused by a human coronavirus (CoV) named SARS-CoV. SARS-CoV emerged from zoonotic precursor viruses by a mechanism that is not fully understood, but likely involved a commonly used viral replication mechanism, homologous recombination, during co-infection of multiple host species. The emergence and rapid global spread of SARS-CoV underscores the importance of developing stable vaccines and therapeutics for this family of viruses. Our laboratory has shown that remodeling the SARS-CoV subgenomic transcription regulatory network (TRN) allows the production of infectious virus, and that generation of theoretical recombinants of remodeled TRN viruses and wildtype TRN viruses abolishes virus replication. Further, we have preliminary evidence that TRN remodeled viruses are attenuated for disease in mouse models and that TRN remodeled viruses are protective against pathogenic heterologous SARS-CoV challenge. The goals of this proposal include: defining the mechanism(s) by which remodeling of TRNs attenuates SARS-CoV virulence and pathogenesis;and determining the role(s) of replicase and/or accessory proteins in SARS-CoV virulence and pathogenesis. This proposal outlines experiments that will use viral reverse genetics, site-directed mutegenesis, in vitro biochemical assays, and viral inoculation of young and old mice to address these goals. PUBLIC HEALTH RELEVANCE: The studies outlined in this proposal will further our knowledge of how coronaviruses replicate and cause disease in host organisms and will facilitate the rational design of viral-based vaccines and therapeutics.